1. Field of the Invention
This invention relates to 2,5-reactive substituent group-containing siloles which are novel .pi.-electron conjugated organic compounds having a light absorption band or bands in the range of UV to visible light, and also to polycondensates and intermediates thereof. The invention also relates to processes for preparing such siloles, polycondensates and intermediates as set out above.
2. Description of the Prior Art
Highly stable polymers such as polyacetylene, polythiophene, polypyrrole and the like have been hitherto reported as .pi.-electron conjugated organic polymers and their development for use as organic conductive materials has been studied. In recent years, aside from the homopolymers, there have been prepared various copolymers such as of combinations of thiophene and pyrrole. Attention has been drawn to these materials, with the possibility that they are applicable as a new functional material in view of their unique light absorption spectra ascribed to the intramolecular donative and acceptive structure of electrons.
On the other hand, polymerization of siloles has been studied because the silole skeleton has a structure serving as both an electron donor and an electron acceptor. We have already proposed in Japanese Patent Application Nos. 4-196609 and 5-82620 copolymers having both a silole structure and a thiophene structure, with the expectation that such polymers can be applied as an optical functional material owing to the very unique light absorption characteristics thereof. In this connection, Barton et al has shown that according to the theoretical calculation, the polysilole bonded at the 2,5 positions has a possibility of providing a polymer whose non-linear optical characteristics are good. Moreover, Frapper et al reported that such a polysilole as mentioned above has so small a band gap that there is a high possibility for use as a conductive material. However, hitherto known processes involve a difficulty in introducing reactive groups into silole compounds at the 2,5 positions. Satisfactory studies have never been made on the preparation of 2,5-reactive substituent-containing siloles up to now, with the exception that Wrackmeyer et al (Chem. Comm., 86, 397) reported the preparation of siloles having a boron substituent at the 3 position and two stannyl substituents at the 2,5 positions by reaction between bis(2-stannylethynyl)silane and boranes.